South Capitol Street Corridor

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The two-phase, nearly $1 billion project will restore this DC corridor to the symbolic gateway envisioned in Pierre L’Enfant’s original plan of 1791. The first phase of the project is nearing completion and includes: Replacement of the Frederick Douglass Memorial Bridge, two approach ovals east and west of the Anacostia River, replacement of the I-295/Suitland Parkway Interchange, reconstruction of the I-295 overpasses at Howard Road and Firth Sterling Avenue and construction of several traffic ramps.

How did we help?

As part of the Walsh/Granite/AECOM team, ECS completed geotechnical engineering analysis and construction phase support services for landside structures including: Three I-295 interchanges retaining walls, roadway embankments and subgrade, pedestrian tunnel, stormwater management ponds, signal poles, ground improvements and existing utility protection. The field program consisted of 250+ explorations: SPT borings, CPTu, DMT and PMT in-situ tests, infiltration tests, vibration monitoring points and pre-/post-construction surveys.

What unique challenges did we face?

The South Capitol Street Corridor project site sits on a challenging and varying soil geology with heterogeneous soft soil conditions in several key locations of the project that posed critical geotechnical evaluation of foundation design, roadway embankment, retaining wall stability and settlement considerations.

A series of ground improvement methodologies, structural support slabs, lightweight fills and instrumentation and monitoring were used in tandem to meet project settlement and loading criteria in key locations across the project site. Large, aging and fragile infrastructure criss-crosses the alignment and protection measures were developed in order to protect these assets and to ensure their undisturbed operation.